18 replies to this topic

[ZE.FT]

I do remember one of the cars which raced in LeMans few years ago was equipped with a front difuser and a rear difuser.Toyota GT One?

As back difusers are getting more and more common within the new road sport car generation,

1.Is somebody out there who can name a road car which is equipped with a rear AND a front difuser?Propably it should be a mid engine placed car, or a front engine which is placed pretty to the middle of the car like Mercedes SLR or Corvette or TVR?
2.Will there be a drop in the rear difuser downforce figures with such an application and if so appr
how much should be expected?

[TOPCAT1976]

Came across this - http://www.topcat1976.com/enzo.jpg

Is that not a diffuser at the front of the Enzo?

[scarbs]

I dont think the Enzo has a diffuser as such, the raised nose forms more of a channel feeding the floor and the rear diffuser.
The only road car that I know that has some form of front downforce device is the McLaren F1. which both vents the front floor through the sidevents and through the top of the bonnet.

You do of course have the even madder Mercedes CLK GTR or Porsche GT1, but these are simply race cars adapted to the road.

[ZE.FT]

I also tend to say that on the photo link from TOPCAT the tunnel in the middle isnt the front difuser
just from the shape it has .Would it be turned around and the front wider side would show to the rear end of the car I would have said yes,this is it.
I must add that I do not know what it is and tend to guess in scarbs direction.

[desmo]

Wouldn't a front diffuser necessarily rob the undercar flow of its dynamic pressure component, compromising the effectiveness of a rear diffuser? Further, road cars hardly need aero downforce, it will create unneccessary drag and compromise packaging as well. Wings and diffusers on road cars strike me as more boy racer styling licks than as real functional devices in the vast majority of instance. Something resembling such an aero device might be useful for countering lift from poorly designed bodywork, but surely it is a manifestly bad idea to be driving on open roads at the sorts of speeds where aero downforce could be useful to cornering.

[OO7]

Originally posted by desmo
Wouldn't a front diffuser necessarily rob the undercar flow of its dynamic pressure component, compromising the effectiveness of a rear diffuser? Further, road cars hardly need aero downforce, it will create unneccessary drag and compromise packaging as well. Wings and diffusers on road cars strike me as more boy racer styling licks than as real functional devices in the vast majority of instance. Something resembling such an aero device might be useful for countering lift from poorly designed bodywork, but surely it is a manifestly bad idea to be driving on open roads at the sorts of speeds where aero downforce could be useful to cornering.

Hi Desmo

This is something I've considered before, but sportcars such as the Audi R8 etc do feature front diffusers. Audi R8 front diffuser
2003 Bentley front diffuser details
I've heard that sportscars inherently suffer from understeer and with pre-04 regs deleting a front diffuser would mean nealy all downforce is focused about the rear axle at high speed zero rake. Perhaps including a front diffuser and compromising the rear offers the best solution of increased downforce and aero balance?.

Obi

[ZE.FT]

From the samples given at mulsannescorner I see that a king size front splitter is used together with the front diffuser which seems of help for increased front diffuser downforce.

[zac510]

ZE.FT , what is the principle with the big front splitter and front diffuser? Is the big underbody surface area ahead of the front diffuser what makes the diffuser efficient?

[ZE.FT]

zac510, I'm not an expert here.But having studied some CFD files on front splitters on closed wheel racing cars it seems that as you say the longer way of the air beyond the frontal splitter and underbody is what seems make the front diffuser work.I also do remember having noticed that even before the air gets into the diffuser a low pressure zone is created just under the front splitter.
But again there are experts here which may explain this in a better way or correct me if I'm wrong.
Honestly said,I would have expected any comments also on the interaction of the front/rear diffusers.We still may get them.
Rgds

[OO7]

Originally posted by ZE.FT
I do remember one of the cars which raced in LeMans few years ago was equipped with a front difuser and a rear difuser.Toyota GT One?

As back difusers are getting more and more common within the new road sport car generation,

1.Is somebody out there who can name a road car which is equipped with a rear AND a front difuser?Propably it should be a mid engine placed car, or a front engine which is placed pretty to the middle of the car like Mercedes SLR or Corvette or TVR?
2.Will there be a drop in the rear difuser downforce figures with such an application and if so appr
how much should be expected?

ZE.FT

I forgot to mention the Saleen S7 even in road car guise, does have both a front and rear diffuser. There was a programme on discovery about supercars or ultimate cars a few weeks back and the S7 was one of the featured cars. One of the engineers presented a CAD design of the S7 underbody.

Obi

[ZE.FT]

Obi,thanks for posting and the sources

[OO7]

Originally posted by ZE.FT
Obi,thanks for posting and the sources

No Probs

The show was just repeated Friday or Saturady afternoon on the Discovery channel.

BTW the Ferrari Enzo sort of has a front diffuser, one ahead of each front wheel. They are active devices and work in unison with the rear spoiler.

Ferrari Enzo underbody There was a high-res image of the Enzo underbody on the net but I can't find it unfortunately.

Obi

[LMP900]

Originally posted by desmo
Wouldn't a front diffuser necessarily rob the undercar flow of its dynamic pressure component, compromising the effectiveness of a rear diffuser?

Yes it would. But for racing Prototypes and for road cars there is another legal and reasonably efficient means of getting rear downforce than by using the rear underbody: not so for the front.

[shaun979]

Hi Andy, what is this legal and reasonably efficient means you speak of? Are you referring to a rear wing? I always thought it is far less efficient than using the rear underbody? Is there anything besides these two options? Curious... thanks

[LMP900]

shaun - yes, I do mean the rear wing. A prototype's rear wing has a relatively high aspect ratio (2m wide), so is a pretty efficient device, whereas its diffuser is (or was, 2 years ago when I posted!) limited by starting at the rear axle centreline, by having a maximum height at the trailing edge, and having to have flat and longitudinally aligned strakes.

[Goran Malmberg]

Originally posted by LMP900
Yes it would. But for racing Prototypes and for road cars there is another legal and reasonably efficient means of getting rear downforce than by using the rear underbody: not so for the front.

Lets see what you think of my idea here. I am building a Nordic Supercar Corvette that has a front diffuser that might be of interest. The car has one big air outlet each side, aft of the front wheel, for the front diffuser air to escape. Front diffuser contains of tree (main) sections. One middle section that is adjustable
from closed (in line with the underside), to fulley open to the same level as the two side sections that are fixed in open possition to the side outlets. That way I am hoping to Balance underside downforce front to rear. The rear diffuser is possible to expand in the same manner but even regarding to the curvature. If there is an interest I will present a report as soon as I have been testing the car. There are a few images om my site http://www.hemipanter.se/ fare down the site. Dont mind the look of the rear diffuser, its just a mock up.
Regards
Goran Malmberg

[LMP900]

Originally posted by Goran Malmberg


Lets see what you think of my idea here. I am building a Nordic Supercar Corvette that has a front diffuser that might be of interest. The car has one big air outlet each side, aft of the front wheel, for the front diffuser air to escape. Front diffuser contains of tree (main) sections. One middle section that is adjustable
from closed (in line with the underside), to fulley open to the same level as the two side sections that are fixed in open possition to the side outlets. That way I am hoping to Balance underside downforce front to rear. The rear diffuser is possible to expand in the same manner but even regarding to the curvature. If there is an interest I will present a report as soon as I have been testing the car. There are a few images om my site http://www.hemipanter.se/ fare down the site. Dont mind the look of the rear diffuser, its just a mock up.
Regards
Goran Malmberg

I can't get much detail of the front diffuser from your website Goran, but you certainly have a large enough extractor to make it work! It may be too large - I always found that a controlled expansion of the duct cross-section, from the venturi throat through to where it rejoins the general flow, gave better results than a gaping hole: the air speed decelerates gradually rather than stalls.

I'm not clear where the air from the centre section of the diffuser goes if it's set to maximum - presumably it has to flow around the engine, and out through the same exit ducts as the outer diffusers.

I'd be interested to hear how you get on in testing, and I'd suggest two things - that you use plenty of strakes (flow dividers along the direction of flow) to limit crossflow due to spanwise pressure differential, and you try throttling down the exit duct when you have the centre diffuser set at minimum.

[Goran Malmberg]

Andy,
There is not much details on my site, it just thought it might give an idea about what I am doing. If you check out the font of the chassis, and also the very small drawing behind myself, you will find that the front of the engine is in line with the rear of the front wheels. The lower front frame tubes is some 4 inches over the underside so the front engine mounting plate (Beside from triangulating function) sticks down also supporting bellypan. Under the front section of the frame (4 inches bellypan to frame) and in front of the engine mounting plate, there is an air dewider directing middle section diffuser air out the side outlets.
Side outlet will also handle some engine compartment venting, but a bit longer back the side outlets, near the fire wall. Not seen on those images.
The upper portion of the side outlet will handle radiator air.
Regards
Goran Malmberg

[jmorris]

Take a look at the NASCAR COT or many racing touring cars. That flat horizontal black plate on the bottom of the 'bumper" is a diffuser.
Clean air is squeezed through the small gap between the bottom of that plate and the road surface, as this air speeds up to get through that gap the pressure drops pulling down on the bottom of the plate. Prototype sports cars do the same thing but with a more complex and larger shape under the front 1/3 of the car.